The present invention relates to a process and a device for injecting a liquid agent used for treating a geological formation in the vicinity of a well bore traversing this formation.
Devices using hydraulic jets are already known (for example from U.S. Pat. No. 3,892,284) to enable boring and cutting of tubings, as well as cleaning of geological formations by abrasion, optionally combined with a chemical attack.
These devices deliver very concentrated jets, for creating a very precise local effect (for example cutting off a slot in a tubing).
In contradistinction to these destructive techniques, the invention is in particular applicable to the consolidation of geological layers or formations traversed by the well bore, over a substantially great height thereof which may usually reach several meters, and may even exceed 10 meters, by injection of resins or siccative oils. The invention is also applicable to the acidification of some of the traversed ground formations, etc.
Consolidating processes are already well known wherein a liquid-air mixture is prepared to create a foam at the level of the formation, this foam serving either to position solid particles in the formation (U.S. Pat. No. 3,602,398), or to control losses of drilling fluid (U.S. Pat. No. 3,637,019). However the latter process has the disadvantage of suppressing the permeability of the geological formation.
The invention pertains, in particular, to any treatment in the vicinity of a well bore for the purpose of consolidating a geological formation without substantially reducing its permeability, such as for example, a treatment for consolidating a well-surrounding gas-containing and optionally oil-containing geological formation by injection of a reacting liquid over the entire height of the formation.
Up to now consolidation of geological formations by injection of resins has been effected either by means of resins containing a hardening catalyst, or by successively injecting a catalyst-free resin and then a plug of catalyst-containing fluid. The first operating mode can result in the plugging or clogging of some pores of the formation.
When selecting the second operating mode, there is a risk that the two injected liquids will not be positioned at the same level of the formation.
A prior art process for treating a geological formation (consolidation treatment, for example) comprises the following two steps: (a) a first step of injecting a suitable liquid (optionally diluted by a solvent, as taught in U.S. Pat. No. 3,330,350) into the ground layer, and (b) a second step of injecting a gas through this liquid, so as to prevent total plugging of the formation pores. The injected gas may optionally be a gas which reacts upon contact with the traversed liquid.
Prior to the liquid injection, it will optionally be possible to inject suitable scavenging fluids so as to displace the crude oil or water, or to stabilize the clays which are present in the geological formations.
The first step, i.e. positioning of the treating liquid in the formation, can be achieved by simply pumping the liquid into the well. However this mode of operation suffers from a major drawback when treating very permeable geological formations, particularly gas-containing formations, because the liquid tends to mainly to flood the lower level of the ground layer.
On the contrary, the gas injected during the second step of the process has a tendency to flow between the upper level of the liquid and the top of the ground layer.
Another prior art method, described in U.S. Pat. No. 4,119,150 comprises locally injecting a foaming resin which solidifies or sets in situ. It is however difficult with such a method to control the permeability of the formations consolidated by this resin. As a matter of fact, the foam is formed essentially of gas bubbles separated by walls of solidified resin and it is always difficult to provide these walls the desired permeability relative to the gas and liquids which are present in the formation.